U.S. Pat. No. 5,014,668 discloses at least partially driving an internal combustion engine with a lean air/fuel mixture. The air/fuel mixture signal is determined from the measured engine load (air mass, air quantity or intake pipe pressure) and the engine rpm. To form the fuel injection pulse, the air/fuel mixture signal is corrected with the pregiven desired value for the air/fuel ratio as well as with an output signal of a control unit. This control unit forms a control loop for adjusting the pregiven desired value for the air/fuel mixture. Furthermore, in the known control of the internal combustion engine, the air supply to the engine is adjusted in dependence upon the driver command by means of an electrically actuable power adjusting device such as an electrically actuable throttle flap.
For controls of this kind, a fuel quantity, which is increased with respect to the correct desired value, leads to impermissible torque increases. The increased fuel quantity can be a consequence of: an error in the detection of load (air mass measurement, air quantity measurement or intake pipe pressure measurement); an error in the air/fuel ratio control loop (such as a probe fault); an error in the signal processing in the electronic control apparatus; or, an error in the battery voltage correction of the injection time.
Here it should be noted that a fault in the detection of load, even for the conventional operation of an engine with a stoichiometric mixture, can lead to an impermissible increase of the engine torque. If, for example, the air mass sensor measures an air/fuel mixture signal which is too small (for example, too small by a factor of 1.5), the mixture would become too lean without mixture control and/or elevation adaption and the engine torque would, in this way, be rather too small than too great. However, conventional controls are equipped with mixture controllers and/or elevation adaption. For this reason, these functions compensate for the air mass error within their pregiven limits. The functions ensure that an essentially normal engine operation is provided notwithstanding this fault. If the situation develops that this dormant error in the air/fuel mixture signal is accompanied by an impermissible opening of the throttle flap in a system having electrical adjustment of the throttle flap, so that the air/fuel mixture increases, for example, by a factor of 1.5, this can lead to a non-detected increase of the engine torque by approximately this factor 1.5. This takes place when the monitoring of the electric control of the throttle flap is not carried out on the basis of the position signal but on the basis of an actual engine torque computed from the air/fuel mixture signal which is too small.
Measures for error detection are not described in the above-mentioned state of the art.
German patent publication 4,243,449 discloses an electronic control system for metering fuel to an internal combustion engine wherein the air/fuel mixture signal is corrected by a corrective signal for transition compensation (wall film correction). The corrected air/fuel mixture signal is, in turn, subjected to a further correction with respect to battery voltage to form the actual injection time. Measures for error detection are also not disclosed.